This project is involved with the generation of thymus derived immunologically competent and active cells. Three lines of approach are used: 1) Testing for tumor analogues of thymus derived cells, in order to obtain large populations of homogeneous (cloned) cells for detailed study of T cell surface receptors for antigens. 2) Development and purification of antisera specific for lymphocyte subpopulations of the B cell (bursal) and T cell (thymic) lineage; 3) Use of these antisera to aid in definition of the various morphological substructures in peripheral lymphoid tissues, as well as aiding the definition of T cell and B cell functions in cellular immunity.